Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.47	3.533%	$30.5112	$30.51	$30.50	$30.50
Purchase #2	$40.78	8.809%	$44.3723	$44.37	$44.35	$44.40
Purchase #3	$28.36	9.575%	$31.0755	$31.08	$31.10	$31.10
Purchase #4	$40.55	4.480%	$42.3666	$42.37	$42.35	$42.40
Purchase #5	$107.71	5.347%	$113.4693	$113.47	$113.45	$113.50
Purchase #6	$195.93	7.851%	$211.3125	$211.31	$211.30	$211.30
Purchase #7	$171.31	12.344%	$192.4565	$192.46	$192.45	$192.50
7 purchase totals =	$614.11		$665.5639	$665.57	$665.50	$665.70